2968 Integration of PET / MR hybrid imaging into radiation therapy treatment planning

Purpose: Magnetic resonance (MR) imaging has become an important part in radiation therapy (RT) treatment planning. Excellent soft tissue contrast and the potential use of functional imaging can improve the accuracy of target volume delineation [1]. Furthermore, positron emission tomography (PET) is increasingly used as an additional imaging modality [2]. Integrated PET/MR combines both modalities and might play an important role in future when it comes to exact RT planning [3]. For accurate patient positioning during PET/MR acquisitions, a flat RT overlay and positioning aids are necessary that have to be MRand PET-compatible. While carbon fiber-based tabletops used for CT imaging are not MR compatible, MR tabletops mostly consist of high attenuating glass fibers, which dramatically reduce the PET signal and might produce PET image artifacts. Furthermore, local radiofrequency (RF) coils have to be used for high quality MR imaging without touching and deforming the surface of the patient. Thus, coil holders (CH) are usually used in MR-based RT planning that have to be optimized towards photon attenuation if used in PET/MR imaging. In this work, a flat prototype RT overlay and CHs for head imaging are introduced that are suitable for patient positioning in hybrid PET/MR imaging. Both devices have been evaluated towards PET and MR compatibility. MR image quality has been tested and compared to the actual PET/MR setup. PET photon attenuation has been evaluated by phantom scans and attenuation correction (AC) methods of both devices are presented. Usage of the new RT setup in PET/MR imaging has also been illustrated with an in vivo study on two patients.